The invention set forth in this specification pertains to new and improved pipe plugs.
Pipe plugs of the type to which this invention pertains can be used in closing off the ends of pipes so as to prevent the interiors of such pipes from becoming contaminated. They are more often used to close off the ends of pipes so that the interior a pipe or of a piping system can be tested for leakage under pressure. It is considered a matter of common knowledge in the plumbing field that a variety of internally fitting plugs and externally fitting end caps can be used for closing off the interior of an end of a pipe. Normally it is considered advisable to use internally fitting plugs to close off the ends of pipes of a comparatively large diameter.
As technology pertaining to the use of polymer pipes has advanced and as labor costs have increased, a particular type of internally fitting pipe plug has been increasingly used. Plugs of the latter type are constructed so as to each include an elastomeric, expandable sleeve which can be easily inserted within a pipe and then expanded so as to form a seal with the interior of the pipe and what may be referred to as a one piece, plug-like, rigid expander which fits with the sleeve in such a manner that it can be turned or rotated relative to the sleeve so as to expand the sleeve. Pipe plugs of this category are significantly less complex and less expensive than other types of plugs formed so as to apply pressure generally towards the opposite ends of the sleeve to expand the sleeve.
In plugs using only an expandable sleeve and a one piece expander, it has been customary to form the sleeve so that its exterior is cylindrical and so that it has a tapered, internally threaded surface and to form the expander so that it has a correspondingly tapered and threaded surface and a centrally located means such as a square stud for engaging the expander with a wrench so as to turn it relative to the sleeve in order to expand the sleeve within the interior of the end of a pipe. Pipe plugs constructed in the manner have proved to be highly utilitarian. However, it is considered that in general they are not as desirable as might be desired.
Most commonly, the exteriors of the sleeves with this type of pipe plugs are substantially smooth cylindrical surfaces which are formed so as to only be slightly less in initial or unstressed external diameter than the internal diameter of a pipe of a size with which the sleeve is designed to be used. In theory such a close match in diameters is desirable since it enables a sleeve alone or an entire plug including the sleeve to be easily inserted in a pipe end and since only a limited amount of expansion is then necessary to bring the sleeve into sealing engagement with the interior of a pipe. Unfortunately it is believed that in some circumstances surface irregularities either at the periphery of the sleeve or in that interior of the pipe or as a result of a contaminate particle being present will tend to interfere with sealing action achieved.
Obviously the latter is undesirable. It is also considered that the prior pipe plugs of the type indicated are not as desirable as reasonably possible since normally they have been constructed so that they can only serve one function--that of sealing the end of a pipe. While there is nothing wrong with this, at times the fact that a pipe plug can only be used for sealing purposes is undesirable. This is particularly the case when there is no reasonably convenient, apparent manner of pressurizing the interior of a pipe so as to test against leakage or of mounting a gauge so as determine the internal pressure within a pipe or piping "system".